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Retention of calcium carbonate in mechanical pulp suspensions Modgi, Sivamurthy B.


This work investigates the retention of precipitated calcium carbonate (PCC) in thermo-mechanical pulp suspensions using polyethylene oxide (PEO), phenol formaldehyde resin (PFR) system in conjunction with Raifix 120, Raifix 2515 and Raisapac. Raifix is a starch-based polymer produced by Raisio chemicals of Finland. Raisapac is poly hydroxy aluminum chloride and is also manufactured by Raisio chemicals. The PCC used for this work was obtained from Specialty Minerals Inc. and its commercially known as Albafil. To maintain the pH of the PCC loaded pulp suspension to neutral the PCC was treated with phosphoric acid (0.2g/g of PCC). A 10 wt. % PCC suspension was pretreated with phosphoric acid for 24 hours according to the method proposed by Pang (Pang, 2001)and used in the first pass retention experiments. First pass retention experiments were performed using a Britt dynamic drainage jar. A 0.5% pulp suspension was loaded with 20% of pretreated PCC (10 wt.%). At first the retention experiments were done with only PEO and PFR at a PEO dosage of 0.15 mg/g of OD pulp. The retention of fines and pretreated PCC increased by 27% and 62% respectively at a PEO, PFR ratio of 1. Retention experiments were then performed with Raifix (120 or 2515) in conjunction with the PEO, PFR system. The best sequence of addition using Raifix was found to be Raifix-PCC-PFR-PEO. A 32 statistical design of experiments showed that there is a significant interaction between PEO, PFR and Raifix. This interaction was manifested as an increase in retention at a dosage of 0.05 mg/g of PEO, PFR, but decreased at a PEO, PFR dosage of 0.15 mg/g of OD pulp. It is believed that Raifix scavenges PFR and therefore interferes with retention. The sequence used for first pass retention with Raisapac was Raisapac, PCC, PFR and PEO. The retention obtained using Raisapac was greater than that using Raifix but similar to that obtained by PEO, PFR. The effect of DDJ stirrer speed at various rpm was performed with the best retention conditions for PEO, PFR system, Raifix-PEO-PFR and Raisapac-PEO-PFR system.

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